The recent introduction of four-wheel and all-wheel drive motor vehicles, including those employing torque-on-demand systems (e.g., BorgWarner Automotive, Inc.'s TOD™ system), has greatly aided in the safety and drivability of these vehicles under sub-optimal road conditions. Some of these types of vehicles also employ a power take-off (PTO) system that is associated with the vehicle's main engine system in order to provide a separate power source to run auxiliary machinery, whether integrated and/or independent, such as mixers, compacters, winches, balers, and the like.
Conventional PTO systems typically include some type of clutch system. Conventional PTO clutch systems typically include an input member, an output member, a clutch pack (e.g., a set of multiple plates or discs), and a control system for selectively engaging the input and output members.
A description of various four wheel drive and torque-on-demand systems can be found with reference to U.S. Pat. No. 5,492,194 to McGinn et al.; U.S. Pat. No. 5,690,002 to Showalter; U.S. Pat. No. 5,839,328 to Showalter; U.S. Pat. No. 5,884,738 to Joslin et al.; and U.S. Pat. No. 5,966,999 to Showalter et al., the entire disclosures of which are incorporated herein by reference.
Because most engine systems used in these types of vehicles can generate far more torque than conventional PTO systems can accept, operators of these vehicles have been keenly aware of the potential damage that can be done to PTO systems by the torque output of the engine system. The most likely cause of damage would occur if the clutch slipped in response to the high torque input level, causing the clutch pack to rapidly overheat, which could then potentially damage the clutch plates. This would then necessitate the time-consuming and costly repair and/or replacement of a portion of, or the entire clutch pack.
Accordingly, it has been suggested that in order to protect the clutch pack, the clutch system temperature must be monitored and the clutch system turned or disabled off before the critical temperature is reached. This can be accomplished by using a temperature sensor to directly measure the temperature of the clutch system.
For example, a temperature sensor can be installed in the clutch assembly to measure the actual temperature of the clutch system. When the measured temperature exceeds the critical temperature, the vehicle's electronic control unit (ECU) would turn off the clutch system until it cools down to an acceptable temperature.
Advantages of such a system would be accurate measurement of clutch system temperature independent of ambient temperature and lube flow and it would allow the ECU to compensate for variations in current due to temperature. Disadvantages of such a system would be the additional cost of sensors and wiring, and if the sensors or wiring failed, the ECU could not protect the clutch system from thermal damage.
Other approaches to solving the above-mentioned problem have also been attempted. Some of these approaches can be found with reference to U.S. Pat. No. 4,484,653 to Horikoshi et al.; U.S. Pat. No. 4,499,450 to Makita; U.S. Pat. No. 5,237,883 to Churchill et al.; U.S. Pat. No. 5,611,751 to Ehrenhardt et al.; U.S. Pat. No. 5,740,044 to Ehrenhardt et al.; and U.S. Pat. No. 5,838,591 to Yamaguchi, the entire disclosures of which are incorporated herein by reference.
Unfortunately, the afore-mentioned approaches do not address the issue of calculating the clutch system temperature without the use of expensive and unreliable temperature sensor systems, but rather focus on other techniques for protecting the clutches of the various PTO-equipped systems.
Therefore, there exists a need for a control system for easily, inexpensively, and reliably calculating the clutch system temperature of a PTO-equipped system so as to be able to selectively and temporarily stop the operation of the clutch system before the clutch system reaches a pre-determined temperature limit, especially for four wheel drive vehicles and more especially for those four wheel drive vehicles employing TOD systems.